The present invention relates to systems and methods for controlling the flow of pressurized fluid and, more specifically, to such systems and methods that allow precise control of flow of fluid from a source having high, variable, and/or unknown pressure.
In many disciplines, a pressurized fluid must be supplied in precise quantities. Usually, the quantity of fluid supplied is controlled by regulating the flow of the fluid. Fluid flow is independent of conduit size, supply pressure, and the like, and controlling the flow rate ensures that a precise quantity of the fluid is delivered where required.
The present invention is of particular significance when used to control the flow of gasses at relatively low flow rates. The present invention also has application to other fluids such as liquids and to relatively large flow rates. The scope of the present invention should thus be determined with reference to the claims appended hereto and not the following detailed description.
One example where the quantity of a gas supplied must be precisely controlled is the delivery of a gas to a medical patient. In this context, a gas is mixed with air supplied to the patient through a ventilator to obtain a desired effect. If too little gas is supplied to the patient, the desired effect may not be obtained. On the other hand, too much gas may be toxic to the patient. Other examples where precise quantities of gas must be supplied include scientific and medical testing, industrial processing, and scuba diving.
A primary impediment to maintaining a constant flow of gas is that the pressure at which the gas is supplied may be unknown or variable. Often, the source of the pressurized gas is a pressurized tank or compressor. The pressure of the fluid supplied by either of these sources can fluctuate significantly. For example, as the quantity of gas within a pressurized tank decreases, the pressure of the fluid flowing from the tank will decrease. Accordingly, in many systems in which the flow of a gas is important, the flow rate must be measured and monitored and the system adjusted as necessary to maintain the flow rate within predetermined limits.
U.S. Pat. No. 4,015,626 issued to the present Applicant discloses a valve assembly for maintaining constant flow rates. This valve assembly comprises a housing that defines upstream and downstream chambers, a movable wall assembly arranged between these chambers, a spring located in the downstream chamber that acts on the movable wall, a bicycle valve located in the upstream chamber such that its control stem engages the movable wall, and coiled high resistance tubing connected between the chambers. Changes in the pressure in the downstream chamber allow the movable wall to move and operate the bicycle valve control stem to open or close the bicycle valve to control the flow of fluid flowing through the valve assembly. The spring may be adjusted to obtain different flow rates. The tubing functions as a pressure reducing restriction and to average the flow rate of fluid passing therethrough.
The valve assembly disclosed in the ""626 patent is relatively complex and expensive to manufacture. Also, the pressure drop through the high resistance tubing plays an important role in determining the range of flow rates that may be obtained. Altering the pressure drop through the tubing to obtain different flow rate ranges would be difficult because different tubing (i.e., change of length or passageway size) must be used. The length of the high resistance tubing supplied renders the system relatively large and increases the likelihood of failure. And this valve assembly is designed to operate only at relatively low (80 to 150) psi.
U.S. Pat. No. 6,026,849 issued on Feb. 22, 2000, to the present Applicant also discloses a regulated flow controller that operates using a source having high, variable, and/or unknown pressure. The systems and methods disclosed in the ""849 patent solved many problems related to supplying fluids, and in particular gasses, at constant flow rate.
However, the need exists for improvements to regulated flow controllers such as are disclosed in the ""849 patent that allow this technology to be applied to specific environments.